Method of detecting an analyte in a sample using semiconductor nanocrystals as a detectable label

A method of detecting a target polynucleotide analyte in a sample containing or suspected of containing the polynucleotide analyte, comprising the steps of:

• (a) providing the sample on a solid support;
• (b) combining with said sample a specific-binding molecule, wherein (i) said specific-binding molecule comprises a first member of a binding pair, (ii) the specific-binding molecule is a polymerase chain reaction (PCR) amplification product, which product comprises said first member of the binding pair, and (iii) said combining is performed under conditions that allow formation of a first complex comprising said specific-binding molecule and said polynucleotide analyte, when present;
• (c) removing any unbound specific-binding molecule;
• (d) combining said first complex with a second member of the binding pair, wherein (i) said second member of the binding pair is linked to a first semiconductor nanocrystal;
• and (ii) said combining is performed under conditions that allow formation of a second complex comprising the first complex and the second member of the binding pair;
• and
• (e) detecting the presence of the second complex, if present, by monitoring a spectral emission mediated by the first semiconductor nanocrystal in the second complex, wherein the emission indicates the presence of polynucleotide analyte in the sample.